Recently, nonoxidizing atmosphere kilns, for example, blast furnaces, have been becoming larger in size. Along with this, operations have become more severe. High pressure operations, operations blowing in fine powder coal, etc. have led to increasing damage to the inner lining refractories.
On the other hand, in particular in blast furnaces, longer service life is being demanded in order to offset the high initial investment. The factor having a major effect on such blast furnace life is the durability of the inner lining materials at the side walls and bottom of the blast furnace hearth. As the inner lining materials for such locations, carbonaceous refractories are being used. That is, improvement of the durability of the carbonaceous refractories which are used as inner lining materials would have a direct effect of prolongation of blast furnace life.
Therefore, up until now, numerous proposals have been made regarding the formulation, production conditions, methods of use, etc. of carbonaceous refractories for prolonging blast furnace life.
For example, PLT 1 discloses a method of production of a carbonaceous refractory for blast furnace use comprising mixing metal silicon fine powder with a carbonaceous aggregate and firing the molded product in coke breeze so as to cause a reaction with the N2 or CO gas which is present in the pores of the molded product, form Si—O—N-based whiskers in the pores, and reduce the size of 1 μm or larger pores in which molten pig iron can penetrate and thereby reduce the penetration of molten pig iron or gas into the pores.
Further, PLT 2 discloses a method of adding Al, Si, or other metal powder to a general refractory material to thereby make the structure resulting from the expansion of volume due to production of metal carbides and metal oxides denser, suppress the penetration of oxidizing gas and slag into the refractory structure, and improve the oxidation resistance and corrosion resistance.
Furthermore, PLT 3 discloses the method of adding pitch granules containing Al—Mg and Al—Si alloy and carbon black in carbon-containing unshaped refractories so as to cause the formation of a whisker net in the matrix and thereby improve the hot strength and wear resistance.
PLT 4 discloses, as mud for reducing use of an SiO2-based material, a carbon filler for sealing a blast furnace taphole comprised of an aggregate containing a carbon material, alumina superfine powder, and a metal powder or aluminum and silicon or aluminum in combination to which an organic binder is added, so as to suppress the drop in slag resistance and hot strength of the filler (mud) for sealing a blast furnace taphole, and discloses to use carbon black with its small absorption of iodine for part of the carbon material.
PLTs 5 and 6 disclose carbonaceous refractories containing carbon, alumina, metal silicon, and one or more of titanium carbide, metal titanium, titanium nitride, and titanium carbonitride for balancing the slag resistance and melt loss resistance. That is, addition of alumina to a carbonaceous refractory is effective for melt loss resistance and contributes to reduction of the consumption rate, but excessive addition causes a drop in the slag resistance, so from the viewpoint of balancing the melt loss resistance and slag resistance, the amount of addition of alumina is kept to an extent not causing a drop in the slag resistance and the insufficient extent of slag resistance is secured by adding metal titanium or a titanium compound.
Further, PLTs 5 and 6 disclose, as carbonaceous refractories which are suitable for the inner linings of side walls and bottoms of blast furnace basins, carbonaceous refractories comprised of mixtures of a carbonaceous material, alumina fine powder, metal silicon fine powder, and one or more of titanium powder, titanium nitride powder, and titanium carbonitride powder to which an organic binder is added and kneaded, shaped, and fired in a nonoxidizing atmosphere.